A wind farm is a long, spread-out load, and it does not behave like a factory. Power starts at the turbine, rises to a collector voltage, travels along a string of buried cables and leaves at one grid connection point. Along the way there are two places where a compact substation earns its keep: the collection point that gathers the strings, and the auxiliary supply that runs the substation itself, the control building and the site services. The rest of this note is about how those two are specified – the collector voltage, the transformer rating against a load that is rarely what the nameplate says, and the enclosure against the weather the site actually gets. It is written for the people buying for a wind power project, not for the turbine supplier.
Where the Compact Substation Sits
Each turbine has a transformer that lifts its output to the collector voltage. Several turbines share a string, several strings come together at a collection point, and the collection point feeds the farm’s grid connection. The compact unit we build is the one at that collection point or on the auxiliary side: medium-voltage switchgear, the transformer and the low-voltage board in one enclosure, wired and tested before it leaves the workshop.
The grid step-up transformer that connects the farm to the transmission network is a separate piece of equipment and a separate scope. We stay on the collector and auxiliary side, up to 33 kV, which keeps what we supply inside the range we build and test every day.
Collector Voltage: Why 33 kV Keeps Coming Up
The collector voltage is usually set by the grid operator’s connection code and by how far the strings have to run. Higher voltage means lower current, a smaller cable cross-section and lower losses over distance, which is why 33 kV appears in so many farm designs. Some networks specify 22 kV instead.
We do not pick that number for you. We build the switchgear, the transformer and the board to the voltage the project names, across the range we work to: 6, 10, 11, 20, 22, 33 and 35 kV. On the MV side of a collection point, ring main units are what the layout usually calls for, and they sit in the same enclosure as the rest. Our switchgear range is built around that kind of duty.
Rating the Transformer for a Variable Load
A turbine nameplate is a peak, not a duty. The rating that matters for the collector transformer is the highest simultaneous output the collection point can actually see, which is the sum of the turbines behind it with diversity applied – the whole string is rarely at full output at once. We size it from the farm layout and the load list you send, not by adding up nameplates.
Thermal class, cooling arrangement and losses are then set against the standard the project names. On the auxiliary side the unit is smaller and steadier: substation services, lighting and heating, SCADA and the operations building. That side is usually best handled as a complete transformer substation package rather than as separate pieces bought from separate suppliers.
Enclosure and Environment
Wind sites are chosen for the wind, which usually means exposed. Coastal farms get salt, northern sites get low winter temperatures, plateau sites get altitude and strong sun, and most get dust. Each of those is a different specification: coating system and fixings for salt, heaters and low-temperature materials for cold, de-rating and clearances for altitude, filtered and protected ventilation for dust.
The enclosure rating, the ventilation and the anti-condensation heaters are specified from the site conditions you give us, not assumed from a catalogue. That is why the first thing we ask for after the diagram is the location.
Getting the Unit to Site
Remote sites have their own constraints: single-track roads, weight-limited bridges, and a crane that has to be hired for the day. A compact unit arrives as one factory-built assembly where access allows, and is split into transportable sections where it does not.
We ask about the route at quotation stage rather than discovering it at delivery, because the answer changes the way the unit is built. A unit that has to be split is designed to be split from the start – the joints, the busbar connections and the testing plan all follow from that.
What Testing Happens Before It Ships
Every unit gets its routine tests to the standard the project names, and the reports travel with the equipment alongside the general arrangement drawings and the manuals. Where a client wants to witness testing, that is arranged before the unit is scheduled rather than requested on the day.
The point of testing in the workshop is that faults are found where they can be fixed quickly, with the tools and the spares to hand, instead of on an exposed site in bad weather. Our testing and quality control pages set out what each unit goes through.
Frequently Asked Questions
Can one compact substation serve a whole wind farm?
It depends on the layout and the capacity. Larger farms usually have several collection points, each with its own unit, rather than one large one. We size the arrangement from the single-line diagram and the farm layout you send, and tell you where splitting it makes more sense than one larger unit.
What collector voltages do you build to?
6, 10, 11, 20, 22, 33 and 35 kV. We build to the voltage and to the standard the project names; we do not set the collector voltage for you, because that belongs to the connection agreement.
Do you supply the grid step-up transformer?
No. Anything above 35 kV is a separate scope and a separate piece of equipment. Our units sit on the collector and auxiliary side, up to 33 kV, which is the range we build and test.
How do you handle coastal sites?
Through the coating system, the enclosure rating, filtered and protected ventilation, anti-condensation heaters, and treated or stainless fixings. Which of those a site needs is decided from the conditions you give us, including distance from the shore and the ambient range.
Can the unit be split for transport?
Yes, where the route requires it. Tell us the restrictions at quotation stage – road class, bridge limits, crane availability – and we design the unit to be moved and joined on site, with the joints tested in the workshop first.
Send the single-line diagram, the farm layout and load list, the collector voltage, the site conditions – altitude, ambient range, coastal or inland – and any grid code requirements. We come back with a proposed arrangement, the standard set we would work to, and a quotation. Email info@xsdfftransformer.com or call +8615867897761.